Microwave excited spectrum tube with internal heater



Aug. 7, 1962 E. PAUL, JR

MICROWAVE EXCTTED SPECTRUM TUBE WITH INTERNAL HEATER Filed March 22, 1960 nn nnnnnnn FIGJ FIG. 2

INVENTOR EDWARD PAUL, JR

ATTORNEYS United States Patent 3,048,738 MICROWAVE EXCITED SPECTRUM TUBE WITH INTERNAL HEATER Edward Paul, Jr., Corona, Calif., assignor to the United States of America as represented by the Secretary of the Navy Filed Mar. 22, 1960, Ser. No. 16,898 Claims. (Cl. 313-202) (Granted under Title 35, U.S. Code (1952), sec. 266) The invention herein described may be manufactured and used by or lfor the Government of the United States of America for governmental purposes Without the payment of any royalties thereon or therefor.

The present invention relates to spectrum tubes and more particularly to a new land improved spectrum tube having an internal heater Iand suitable for microwave excitation.

The spectrum tube of the present invention is particularly well suited as a spectroscopy source, and has uses, for example, for: excitation of spectra of newly discovered elements or elements for which spectra are unexplored; controlled stages of excitation, particulary low or rst stages; a source -for excitation of infrequently occurring constituents in spectrochemical analysis; astro-physical problems; identification of elements in extraterrestrial sources by comparison with a laboratory source in the -form of the present device; and, la source of standard wavelength Ifor spectroscopy or metrology favored by principle of operation that leads to output of extremely homogeneous radiation desirable for use with various optical interferometers. In addition, the present device is very well suited for creating unique color effects in display lighting. This invention is also related to copending application vfor Sapphire Spectrum Tube for Microwave Excitation by Curtis J. Humphreys, Serial No. 16,900 filed March 22, 1960.

Previous spectrum tubes consisted of a sealed straight section of glass or silicon tubing into which a suitable quantity of a source material (an element or compound of an element to be excited to show its spectrum) was inserted along with a carrier gas at an appropriate pressure. In order to volatilize the source material to a sufficient vapor pressure that the spectrum could be excited in a microwave beam, heat was applied either by tiaming with a Bunsen burner or by use of furnace incorporating some form of resistance element. The previous spectrum tubes had the disadvantages of: requiring external heating for the volatilization of the source material; non-uniform and ineiiicient heating by -an external source; and, in the instance of use of .an external source for heating, energy is absorbed from the microwave beam which robs the excitation, and external heating is also transmitted to the microwave antenna, the source of the microwave beam, making it necessary to use a cooling device therefor. Also, heating the walls of the spectrum tube in effect sets up a black body which gives a background of continuous radiation, and in turn reduces contrast and suppresses weak lines; in other words, leads to -an unfavorable signal-tonoise ratio. A gas llame from a Bunsen burner or torch produces similar background of continuous radiation arising from incandescent carbon particles always present in a flame, even when it is not noticeably yellow.

The presen-t invention overcomes the aforementioned disadvantages of previous spectrum tubes by employing a heater which fits within the spectrum tube requiring no external connections and provides more uniform and efficient volatilization of the source material.

It is lan object of the invention, therefore, to provide ya new and improved spectrum tube Ifor use as a spectroscopic source.

3,048,738 Patented Aug. 7, 1962 f; 'ICC It is also an object of the invention to provide a new spectrum tube having -an internal heater.

Another object of the invention is to provide a spectrum tube for unique color effects in display lighting.

` A further object of the invention is to provide a new and improved device as a source of standard wavelengths for metrology and spectroscopy.

A still further object of the invention is to provide a new and improved microwave excited spectrum tube having controlled stages of excitation.

Other objects and many of the attendant advantages of this invention will become readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIGURE 1 is a side elevational view of a spectrum tube in accordance with this invention;

FIGURE 2 is a cross-sectional elevational view of the em-bodiment of the invention of FIGURE 1, and

FIGURE 3 is -a cross-sectional View of the embodiment of `the invention of FIGURE 1, taken -along line 3 3.

Referring now to the drawing, like numerals refer to like parts in each of the figures.

A preferred embodiment of the invention for use as a spectrum tube for end-on viewing is shown in the drawings, by way of example, and employs a section of transparent tubing 10 made from quartz or the like yand houses a coil of tungsten wire 12, for example, which fits the inside of tube 10 and is used as a heating unit, the operation of which is more fully described below. The diameter of the wire is not critical, but it is preferred that the diameter of the wire coil 12 be such as to properly lit inside the quartz tube 10 fairly snugly although not fastened thereto. The diameter of the wire, by way of example, maybe .03 or .04 inch, and the length of the coil or wire preferably should be three or more inches. The desired source material is inserted into tube 10. The source material may be any material that has a melting and boiling point within the operable temperature range of the tube. For example, such materials may ybe metals, metal chlorides, -metal iodides. Tube 10` is lled with an inert carrier gas, and it is desirable, though not necessary, to provide a gas reservoir 14 attached to t-he tube to give longer life to the spectrum tube by prolonging reduction of gas pressure by absorption or diffusion. The inside of tu-be 10 is sealed off from the outside atmosphere. A bulb 16, -as illustrated in the drawing, may be provided for end-on viewing, if desired.

In the operation of the spectrum tube of the present invention, the tungsten coil 12 is heated by induced eddy currents when the tube is in a suitable field of microwave energy radiation from a microwave antenna, not shown. This effect is lsimilar to that utilized in an induction furnace. The heat generated in the coil causes the source material to vaporize and produce a vapor pressure therefrom high enough that its spectrum is excited by the microwave beam. The microwave energy rst excites the carrier gas and when the source material vaporizes it -is excited and shows its spectrum. At least a 1200 C. temperature is attainable by this means. Should an even higher temperature be desired, then the ends of the coil of tungsten Wire can be brought out through the quartz tube 10 and an electric current used to heat the coil to -a higher temperature.

The use of an internal heater, such as described herein, may also be used in a `sapphire spectrum tube as disclosed in aforementioned copending application Serial No. 16,900 filed March 22, 1960.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within 3v the scope of the appellded claims the invention may be practiced otherwise than as specically described.

What is claimed is:

1. A spectrum tube for microwave energy excitation comprising a section of transparent tubing made of `glasslike material, a coil of heating element wire completely within said transparent tube operable to be heated to at least 1200 C. by induced eddy currents when -in a suitable eld of microwave energy radiation, a source material to be vaporized by said heating element and microwave excited contained within said tube, the interior of said tube being completely sealed oli from the outside atmosphere and lled with an inert carrier gas, whereby when the spectrum tube is Within a suitable eld of microwave energy radiation said carrier gas rst becomes excited and as the wire and tube become heated the source material will vapor-ize and become excited to show its spectrum.

2. A spectrum tube as in claim 1 wherein said coil of wire is tungsten.

3. A spectrum tube as in claim 1 wherein said coil of Wire fits snugly within the inside diameter of said tube.

4. A spectrum tube as in claim 1 wherein said coil of wire extends over -a major portion of the length of said tube.

5. A spectrum tube as in `claim 1 wherein said tube is made of quartz.

6. A spectrum tube as in claim 1 wherein said carrier gas lling said tube is under pressure.

7. A spectrum tube as in claim 1 wherein said tube has a gas reservoir attached thereto `for maintaining a supply of carrier gas therein under pressure.

8. A spectrum tube as in claim l wherein said tube has an enlarged bulb shaped window at one end thereof for end-on viewing of an excited source material.

9. A spectrum tube for microwave energy radiation excitation comprising a vsection of transparent tubing made of quartz-like material, said tubing containing a coil of tungsten wire operable to be heated to at least 1200 C. by induced eddy currents when in a suitable field of microwave energy radiation and an experimental source material to be vaporized by 1heat from said tungsten coil and microwave excited, the interior of said tubing being completely sealed oi from the outside atmosphere and filled with an inert carrier gas at a desired pressure, whereby when the spectrum tube' is within a suitable field of microwave energy radiation said carrier gas first becomes excited and as the wire and tube become heated said experimental source material will vaporize and become excited to `show its spectrum.

10. A spectrum tube as in 1claim 9 wherein sa-id tube is used for colored display lighting, the colors of the spectrum being determined by the source material used to be excited.

References Cited in the le of this patent UNITED STATES PATENTS 

